Gas dryers produced for sale in the North American Market are usually constructed to operate at a supply voltage of 115-130 volts. The dryer is connected to the electrical supply in order to provide energy to monitor the operation of the dryer, and to operate the timer motor, the gas valve mechanism, the ignition device and the drive motor which turns the drum and drives a blower. Electricity may be used to supply backlighting for the controls as well as illumination in the drum.
When it is desired to construct a gas dryer for foreign markets it will generally be found that in other countries the supply voltage will be in the range of 220-240 volts and that substantial modifications must be made to the standard 120 volt domestic gas dryer in order to have the dryer function at this increased supply voltage level.
The drive motor which turns the drum and blows the air through the dryer during drying periods is usually a standard single phase type using a split-phase scheme to start the motor by methods well known to those skilled in the art.
Drive motors which operate at either of the above voltages are readily available from manufactures thus the drive function is easily converted to the higher voltage. Bulbs and indicating lamps are also readily available for use at the higher mains voltage.
Gas valves and gas igniters which will operate at the higher supply voltage are readily available in countries foreign to North America, but the cost of such modifications which are necessitated by the incorporation of such gas valves and igniters of the higher voltage ratings is great enough to deter a North American manufacturer from using them.
Thus, the standard practice for manufacturers of dryers in North America, in producing clothes dryers for markets which require the higher voltage rating in the past, is to use a step down transformer to lower the voltage applied to the igniter and gas valve in order to provide for operation of a 120 volt dryer at 240 volts. Because the standard ignition device consumes large wattage, it is necessary that the conversion transformer have a substantial KVA rating, thus increasing the cost of conversion of the dryer from the lower voltage level to the higher voltage level.